Compression molded door assembly

ABSTRACT

A door member comprising a frame having a first side and a second side, opposite the first side, a core positioned within the frame, and a molded skin attached to the first side of the frame. The skin is prepared from a molding compound which, when molded, has a shrinkage of between about −0.0003 to about +0.0015. The molding compound comprises a resin system comprising a curable polyester resin, a co-curable unsaturated monomer, and at least two low profile additives. The molding compound also comprises at least about 30 percent by weight, based on the weight of the molding compound, of filler material, and fibrous reinforcement in an amount of less than about 35 weight percent, based on the weight of the molding compound.

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/116,405, filed Jul. 16, 1998, entitled “Compression MoldedDoor Assembly”.

TECHNICAL FIELD

The present invention is directed to a door member, and morespecifically, to a door member having compression molded fiberglass doorskins.

BACKGROUND ART

Door members have been manufactured from solid wood slabs for manyyears. However, solid wood door members have many disadvantages. Forinstance, solid wood door members can experience significant dimensionalchanges with variations in temperature and humidity. This can result incracking and splitting. Also, maintenance of finishes is crucial topreventing degradation of the wood materials. In response, manyconsumers began using doors manufactured from more durable anddimensionally stable materials.

Recent engineering changes in wood doors have made use of laminated woodmaterials and thin surface veneers in an attempt to overcome thedisadvantages associated with solid wood door members. However, newproblems with delamination of the veneers, substrate dimensionalchanges, as well as continuing finishing maintenance are compounded byincreased costs of wood products. This has resulted in door memberproducts that lack consumer acceptance. Thus, the market shares of solidand laminated wood entry doors have continued to decrease.

Steel doors, which superseded wood doors in the market place, hold themajority share of the market, due mostly in part to their low costrelative to wood doors. Steel doors also have the advantage over doorsmade of solid and laminated wood materials of having greater insulationefficiency. Steel doors, however, have many undesirable characteristics.For instance, steel doors dent readily during construction and homeowneruse. Moreover, the surfaces of the steel doors rust, especially when inservice at houses in relative close proximity to salt water, and feelcold to the touch during cold weather conditions.

Fiberglass door members comprising fiberglass reinforced compressionmolded skins have recently become a door member product that hasacquired consumer acceptance. Manufacture of these door members is knownin the art; for example, U.S. Pat. Nos. 4,550,540; 4,720,951; and5,537,789, which are incorporated herein by reference. Fiberglass doormembers typically comprise a door-shaped wooden frame member, apolymeric foam-type core positioned within the frame member, a firstfiberglass reinforced compression molded door skin secured to a firstside of the frame member, and a second fiberglass reinforced compressionmolded door skin secured to a second side, opposite the first side, ofthe frame member. The fiberglass reinforced compression molded doorskins are prepared from a molding compound.

The fiberglass door members compare favorably to wood material doors inthat they are less expensive than wood material doors. Moreover,fiberglass door members overcome the cracking, splitting, delaminatingveneers and poor insulating efficiency associated with wood doors.Furthermore, these fiberglass door members compare favorably to steeldoors in that they resist the denting, rusting and do not have the coldfeel associated with steel doors. However, these fiberglass door membershave, up until now, not been able to be made to have an exterior surfaceas smooth as steel doors or sanded wood doors.

Steel door exterior surfaces are relatively smooth and produce theappearance of a smooth exterior surface when painted. Wood doors, whilehaving relatively coarse exterior surfaces, are sandable, before beingpainted, to produce the appearance of a smooth exterior surface whenpainted. The molded door skins of the prior art fiberglass door membershave been molded to have exterior surfaces which have a very coarse woodgrain pattern to simulate the appearance of a wood door when stained.However, these prior art fiberglass door members, when painted, have theappearance of a painted, unsanded, relatively coarse wood door member.

Many consumers do not find the appearance of such painted fiberglassdoor members aesthetically pleasing. Since, the exterior surface of afiberglass door member cannot be sanded to produce a smooth surface,these consumers purchase wood doors or steel doors if they desire apainted door having a relatively smooth appearance. An apparent solutionmight seem to be to mold the door skins in a mold having smooth faces toproduce door skins having smooth exterior surfaces. However, this hasnot proven to be a solution because the prior art molding compounds arenot capable of producing a surface smooth enough to simulate paintedsteel or sanded wood doors, when painted, due to surface variationscreated in the molding process caused by shrinkage of the molded part.

Accordingly, it is believed that if a fiberglass door member could bemanufactured to simulated steel door members and sanded wood members,when painted, that certain consumer preference for steel door or woodmembers would shift to fiberglass door members. Thus, there is a needfor a fiberglass door member that has a smooth enough surface tosimulate steel and wood door members when painted.

DISCLOSURE OF INVENTION

The present invention is a door member comprising a frame having a firstside and a second side, opposite the first side, a core positionedwithin the frame, and a molded skin attached to the frame. The skin isprepared from a molding compound which, when molded, has a shrinkage ofbetween about −0.0003 to about +0.0015. The molding compound comprises aresin system comprising a curable polyester resin, a co-curableunsaturated monomer, and at least two low profile additives. The moldingcompound further includes at least about 30 percent by weight, based onthe weight of the molding compound, of filler material, and less thanabout 35 weight percent, based on the weight of the molding compound, offibrous reinforcement.

An object of the present invention is to provide a fiberglass doormember that has a smooth enough surface to simulate steel and wood doormembers when painted.

Another object of the present invention is to provide compression moldedfiberglass door skins having a relatively low shrinkage when molded.

These and other objects of the present invention will become moreapparent from a reading of the specification in conjunction with thedrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front elevational view of a door assembly according to thepresent invention;

FIG. 2 is a side elevational view of the door assembly of the presentinvention;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2 showingthe frame of the present invention with the core positioned therein; and

FIG. 4 illustrates the sanding pattern of a conventional multi-panelwood door.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail with referencebeing made to the accompanying drawings. Referring to FIG. 1, a doormember 10 is illustrated. In the preferred embodiments, the door memberis a fiberglass entry way door. Other door members 10 include, but arenot limited to, sidelights, combination entryway door and sidelights,door light frames, door frame, sills and other fiberglass structuralmembers.

Referring to FIGS. 1, 2 and 3, the door 10 includes a core 12 positionedwithin a frame 14. The core 12 is preferably an inserted core or a coreformed in-situ. The core 12 can be made of a variety of materialsdepending on the application. For example, inserted cores can includecontinuous or discontinuous compressed mineral board, compressedinorganic fillers with binders, compressed organic fillers with binders,compressed organic and inorganic blends with binders or in-situ formedbinder; molded or shaped thermoplastics such as expanded polystyrene,foamed polyvinyl chloride, or foamed or expanded polyolefins; molded orshaped thermosets such as flexible or rigid, solid or foamedpolyurethanes, polyurea-urethanes, polyureas, polyisocyanurates, andphenolics; blow molded shells; or honeycomb inserts comprised of organicfibers, organic pulps, thermoplastics, and thermosets; preforms derivedfrom either air-laid or vacuum-laid mats of cellulosic fiber, glassfiber, thermoplastic fiber, or thermoset fiber or woven mats or veil ofthe same materials where a binder or resin has been applied or injectedto shape a core; and blends or mixtures of these various types ofinsertable cores. In-situ formed cores include cores developed fromreaction injection molding with or without reinforcement of thermosetssuch as polyurethanes, polyureaurethanes, polyisocyanurates, andphenolics; gas injection of a thermoplastic, ceramic, or thermoset;activation of in-situ blowing agents or foaming of material introducedinto the shell; mechanical tension applied to melted or softenedthermoplastic or thermoset materials; or blends and combinations ofthese in-situ cores. The choice of a core material is constrained by±10% dimensional change in the range of −40° C. to 95° C. with ±5%preferred. Most preferably, the core 12 is an in-situ core and is madeof polyurethane.

As shown in FIG. 3, the frame 14 includes a first stile 16 and a secondstile 18. The stiles 16 and 18 are parallel to one another. The stiles16 and 18 are positioned in a perpendicular relationship to a first rail20 and a second rail 22, parallel to, and spaced apart from, the firstrail 20. The first and second rails 20 and 22, respectively, extendbetween and connect the stiles 16 and 18. The frame 14 in FIG. 3 has arectangular geometric configuration. However, it should be understoodthat the frame 14 can be arranged in a variety of geometricconfigurations depending upon the desired application.

The stiles 16 and 18 and rails 20 and 22 are preferably made of wood butcould be made of some other suitable material. One of the stiles 16 and18, and preferably, the first stile 16 could be manufactured to addweight to the door 10 to provide the door 10 with a closing momentumwhich makes a person closing the door to believe the door to besubstantial or “solid”. The stile 16 preferably has a width in the rangeof from about 2.5 cm to 16 cm. The stile 16 can also be a hollow channelof pultruded or extruded reinforced plastic, a metal hollow channel, apartially or totally metal reinforced channel made of a material otherthan metal, or a compressed mineral stile depending on the application.

As shown in FIGS. 1 and 2, the door 10 includes a first molded skin 24secured to a first side of the frame 14 and a second molded skin 26secured to a second side of the frame. The skins 24 and 26 of thepresent invention preferably have widths between about 0.75 m and about1.07 m, lengths preferably between about 1.95 m and about 2.45 m, and anaverage thickness between about 1.0 mm and about 2.5 mm and are novel inthat, when painted, simulate the appearance of painted steel or sandedwood doors. As is well known, sanded wood doors typically contain a finelines characteristic of sanding with sandpaper, for example sandpaperhaving grit sizes of 40-150. The fine grooves are generallysubstantially parallel, and with the possible exception of panel endgrain, follow the grain direction of the wood. Door 10 shown in FIG. 4incorporates fine textured sanding pattern aesthetically similar to areal wood multi-panel door which has been sanded smooth with sandpaperin a conventional manner.

The texture of the surface of the skins 24 and 26 is preferablyessentially smooth, such that they can attain a high gloss finish (25-35units) when painted. The texture of the skins 24 and 26 can be made by avariety of casting, machining, polishing, blasting and depositionprocesses. These casting processes include silicone molds, epoxy molds,metal molds from sandcasting, metallic shell on a mandrel, electrolessmetallic disposition on a mandrel and cold isostatic pressing using anyof the above texture transfer techniques to create the textured surfacefor the mandrel. The skins 24 and 26 can be formed with the preferablyessentially smooth texture by many molding techniques including resintransfer molding, vacuum assisted resin intrusion, rotational molding,low and high pressure injection molding, as well as low and highpressure compression molding, with high pressure compression moldingbeing preferred. The door skins 24 and 26 can be larger than the flume14. This allows for the door 10 to be cut squarely, rebated or beveledas required by the user of the door.

The door skins 24 and 26 of the present invention are an improvementover prior art door skins in that they have a much smoother surface thanprior art door skins so that, when painted, they have the appearance ofa painted steel or sanded wood door. In order to produce a fiberglassdoor member 10 which, when painted, has the appearance of painted steelor wood door members, the door skins 24 and 26 should be made using aSMC which can attain a long term Loria® number under about 250 and/or anorange peel Loria® number above about 7.5 as determined by a Loria®surface analyzer.

A Loria® surface analyzer measures the surface smoothness of flatobjects. The Loria® surface analyzer reflects a laser beam off thesurface of a test plaque which has been molded in a mold in which theshow surface had been highly polished to a mirror finish. The plaque istypically about 304.8 mm×304.8 mm. The reflected beam is projected ontoa reflective screen. The image is then picked up off the screen by ahigh-resolution video camera. The laser beam is moved across the surfacein a series of parallel lines. The area of the surface in which thelaser beam is moved across is an area which is sufficient to achieve atrue average of the surface smoothness of the molded plaque, and istypically about 279.44 mm×279.44 mm. The images of these lines are thenanalyzed by the Loria® surface analyzer for smoothness. The Loria®surface analyzer then calculates the long term Loria® number and theorange peel Loria® number for the tested plaque.

The skins 24 and 26 of the present invention preferably have a long termLoria® number of between about 40 to about 200, more preferably betweenabout 60 to about 120, and most preferably of about 100. Moreover, theskins 24 and 26 of the present invention preferably have an orange peelLoria® number of between 8.0 to about 10.0, and most preferably of about9.0.

The present invention achieves the above, and other, goals by providinga molding compound for the door skins 24 and 26 which, when molded, hasa shrinkage of about −0.0003 to about +0.0015 preferably, about −0.0002to about +0.0004, and most preferably about +0.0002. Shrinkage isdefined as the shrinkage or expansion of a cured part as it is comparedto the mold it was molded in. Shrinkage values are obtainable by moldingflat plaques, preferably flat plaques being about 3.2 mm thick with adimension of about 304.8 mm×304.8 mm. The molded part and the mold aremeasured at room temperature. The molded plaques are allowed to set atleast about one day before measuring. Each plaque is measured in fourlocations, two in the transverse and two in the longitudinal direction.Each measurement is divided by the length of the plaque to get theshrinkage value. Positive measurements yield an expansion reading.Negative measurements yield a shrinkage reading. Shrinkage values areunitless since the units cancel and the same reading is obtained whetherit is in./in. or mm/mm.

The molding compounds of the present invention includes sheet moldingcompounds, bulk (or dough) molding compounds, kneading molding compound,thick molding compounds, and injection molding compounds typicallycalled ZMC.

Preferably, the molding compound of the present invention is a sheetmolding compound. The sheet molding compound of the present inventionpreferably comprises a resin system-catalyst component, a thickenercomponent and a fiber reinforcement component. Generally, the resinsystem-catalyst component and the thickener component are preferablycombined first to form a paste. The fiber reinforcement component isthen added to the paste to form the sheet molding compound.

The resin system-catalyst component preferably comprises a resin system,a cure catalyst, a filler material, and an internal lubricant. The resinsystem-catalyst component may preferably also include a cure inhibitor,additional monomer, and an accelerator.

The thickener component preferably includes chemical thickeners toadjust the rheological properties of the sheet molding compound. Thethickener component may further include a monomer, an internallubricant, a cure inhibitor and a pigment.

By the terms “a” and “an” as used herein with respect to a component, orclass of components, of the sheet molding compound, it is meant “one ormore”. For example, the term “a filler material” means that minimallyone filler material is present in the sheet molding compound with two ormore filler materials being optionally present in the sheet moldingcompound. Also, by the term “weight percent” as used herein with respectto a component of the sheet molding compound, it is meant the totalweight of the component and not the weight percent solid of thecomponent, unless otherwise specified.

The molding compound of the present invention preferably comprises fromabout 16.0 to about 33.5 weight percent of the resin system, based onthe weight of the molding compound, and more preferably, from about 21.0to about 29.0 weight percent.

The resin system minimally comprises a curable unsaturated polyesterresin, a co-curable unsaturated monomer and at least two low profileadditive.

The resin system comprises from about 40 to about 75 weight percentsolids, based on the weight of the resin system, and more preferably,from about 48 to about 65 weight percent solids, and most preferablyabout 55 weight percent solids.

Curable unsaturated polyester resins are well known to those skilled inthe art, and are generally prepared in a non-limiting sense, byesterification or transesterification of one or more unsaturateddicarboxylic acids or reactive derivatives thereof with one or morealiphatic or cycloaliphatic diols. Saturated dicarboxylic acids,aromatic dicarboxylic acids, or their reactive derivatives may be usedin conjunction with the unsaturated dicarboxylic acid(s) to lower thecrosslink density. Curable polyester resins are available commercially,and examples of such are disclosed in U.S. Pat. Nos. 3,969,560;4,172,059; 4,491,642; and 4,626,570, which are herein incorporated byreference, and in copending application Ser. No. 09/366,137 entitled“Improved Insulated Door Assembly With Low Thermal Deflection”, alsoincorporated herein by reference.

The curable unsaturated polyester resins may be a high reactivitypolyester resin. Examples of suitable high reactivity polyester resinsinclude, but are not limited to, high reactivity orthophthalic polyesterresins, high reactivity isophthalic polyester resins, and highreactivity dicyclopentadiene-modified (DCPD) polyester resins. Aparticularly preferred curable unsaturated high reactivity polyesterresin is a dicyclopentadiene-modified propylene glycol-maleate polyesterresin.

Co-curable unsaturated monomers are also well known to those skilled inthe art, and include, for example, the various alkylacrylates andalkylmethacrylates as well as vinyltoluene α-methylstyrene,p-methylstyrene, and styrene. By the term “co-curing,” it is meant thatthe monomer contains reactive unsaturation capable of reacting withitself and/or the unsaturated sites of the curable polyester under thecuring conditions. Additional co-curable monomers are identified in theabove-referenced patents. A particularly preferred co-curable monomer isstyrene.

Low profile additives may be defined as relatively polar thermoplasticpolymeric materials which, when added to sheet molding compositions, arebelieved to encourage the formation of numerous microvoids. Suchadditives are believed to become wholly or partially immiscible with theresin matrix during cure under compression molding conditions, resultingin a multi-phasic polymer system. The immiscibility of the low profileadditives may increase the volume of the curing mass, offsetting thevolume reduction of the curing and crosslinking unsaturated components.Moreover, the different phases appear to exhibit different degrees ofcontraction upon cooling. As the compression molded skins cool prior toand after their removal from the mold, the different phases are believedto contract at different rates, which is believed to cause numerousmicrovoids to be created.

Low profile additives are well known to those skilled in the sheetmolding composition art. Low profile additives are generally relativelypolar thermoplastic polymers. While the mechanism of microvoid formationis not known with certainty, it is believed that during the cure of thecurable polyester and co-curable monomer to form a thermoset structure,a microgel phase is formed from the curing/crosslinking of theunsaturated components which is at least partially incompatible with thelow profile additive, which begins to phase-separate. The phaseseparation is believed to cause an increase in volume of the compositionwhich partially or wholly offsets the shrinkage which results fromcuring of the polyester/co-curable monomer. The curing polyester forms amatrix which at least partially surrounds the low profile additivephase. Upon cooling, the differences in volume contraction between thetwo phases is believed to assist in the formation of microvoids. Thepresence of such microvoids may be observed by microscopic inspection ofthe surface, and by the porosity which portions of the surface exhibitwith respect to absorbance of liquids, which otherwise would be minimal.

Examples of suitable low profile additives include, but are not limitedto, polyvinyl acetate, modified polyvinyl acetate, saturated polyester,modified saturated polyester, polymethyl methacrylate, polyurethanes,and styrenic block copolymer-modified rubber. Particularly preferred lowprofile additives are saturated polyesters and polyvinyl acetates, andmore preferably saturated glycol-C₂ to C₆ dicarboxylic acid polyestersand modified polyvinyl acetates. A preferred resin system is availablefrom Alpha/Owens Corning, of Valpairaso, Ind., under the producedesignation E-4295 and comprises a high reactivitydicyclopentadiene-modified propylene glycol-maleate polyester,co-curable styrene monomer, and low profile additives which comprise atleast a saturated glycol-C₂ to C₆ dicarboxylic acid polyester and amodified polyvinyl acetate.

Low shrinkage additives are generally less effective than low profileadditives. They are believed to function by increased phase segregationand immiscibility with respect to the molding resin matrix. Lowshrinkage additives are believed to assist in the formation ofdiscontinuous islands of material which modify the shrinkage propertiesof the molded products. However, they generally do not generatemicrovoids in the molded product. While the use of low shrinkageadditives has been used in molding compounds used to manufacture priorart door skins, low shrinkage additives are not used in the mostpreferred embodiments of the present invention. However, such additivesmay be used with alternative molding systems, for example sheet moldingcompounds based on different base resins. Additional low profileadditives, low shrinkage additives, and other additives may be found inU.S. application Ser. No. 09/366,137, incorporated herein by reference.

The molding compound of the present invention preferably comprises fromabout 0.2 to about 0.9 weight percent of the cure catalyst, based on theweight of the molding compound, and more preferably, from about 0.35 toabout 0.65 weight percent.

The cure catalyst is selected from a list that includes, but is notlimited to, the following:

-   -   diacyl peroxides such as benzoyl peroxide, t-butyl perbenzoate;        t-amyl perbenzoate; ketone peroxides such as mixtures of        peroxides and hydroperoxides; methyl isobutyl ketone peroxide;        2,4 pentanedione peroxide; methyl ethyl ketone peroxide/perester        blend;    -   peroxydicarbonates such as di(n-propyl)peroxydicarbonate,        di(sec-butyl)peroxydicarbonate;        di(2-ethylhexyl)peroxydicarbonate;        Bis(4-t-butyl-cyclohexyl)peroxydicarbonate;        diisopropylperoxydicarbonate; dicetyl peroxydicarbonate;    -   peroxyesters such as alpha-cumyl peroxydecanoate; alpha-cumyl        peroxyneoheptanoate; t-butylperoxyneodecanoate;        t-butylperoxypivalate; 1,5-dimethyl        2,5-di(2-ethylhexanoylperoxy)hexane,        t-butylperoxy-2-ethylhexanoate; t-butylperoxy-isobutyrate;        t-butylperoxymaleic acid, OO-t-butyl-O-isopropyl        monopercarbonate; 2,5-dimethyl-2,5-di(benzoylperoxy)hexane,        t-butylperoxy-acetate; t-butylperoxybenzoate; di-t-butyl        diperoxyphthalate; mixtures of peroxyester and peroxyketal;        t-amylperoxyneodecanoate; t-amylperoxypivalate,        t-amylperoxy(2-ethylhexanoate); t-amylperoxyacetate;        t-amylperoxybenzoate, t-butylperoxy-2-methyl benzoate;    -   dialkylperoxides such as dicumyl peroxide;        2,5-dimethyl-2,5-di(t-butylperoxy)hexane;        2,5-dimethyl-2,5-di(t-butylperoxy)dexyne-3; t-butyl cumyl        peroxide; a-a-bis(t-butylperoxy)diisopropylbenzene; di-t-butyl        peroxide; hydroperoxides such as        2,5=dihydro-peroxy-2,5-dimethylhexane; cumene hydroperoxide;        t-butyl hydroperoxide;    -   peroxyketals such as 1,1-di(t-butylperoxy)        3,3,5-trimethylcyclohexane; 1,1-di(t-butylperoxy)cyclohexane;        ethyl-3,3-di(t-butylperoxy)butyrate; n-butyl        4,4-bis(t-butylperoxy)valerate; cyclic peroxyketal;        1,1-di(t-amylperoxy)cyclohexane; 2,2-di-t-amylperoxy propane.

The preferred cure catalysts are t-butyl perbenzoate; t-amylperbenzoate; 1,5-dimethyl 2,5-di(ethylhexanoylperoxy)hexane;t-butylperoxy-2-ethylhexanoate; OO-t-butyl-O-isopropyl monopercarbonate;2,5-dimethyl-2,5-di(benzoylperoxy)hexane; 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane; 1,1-di(t-butylperoxy)cyclohexane;ethyl-3,3-di(t-butylperoxy)butyrate; 1,1-di(t-amylperoxy)cyclohexane;and 2,2-di-t-amylperoxy propane or combinations thereof.

The molding compound of the present invention preferably comprises fromabout 30.0 to about 70.0 weight percent of filler, based on the weightof the molding compound, and more preferably, from about 40.0 to about65.0 weight percent and even more preferably, from about 45.0 to about59.0 weight percent.

Fillers are principally materials for occupying space, but maycontribute to the mechanical, functional or aesthetic properties of themolded article or door. Suitable fillers include, but are not limitedto, calcium carbonate; magnesium carbonate; aluminum trihydrate;anhydrous calcium sulfate; gypsum; kaolin clays; barium sulfate;nepheline syenite; ground silicas; wollastonite; saw dust; excelsior;minerals with aspect ratio of 4 or less; hollow glass or ceramicmicrospheres; ground agricultural wastes; mixtures of any or all ofthese as well as many others known in the art, including fillers whichhave been treated with coupling agent or low profile agent coatings. Themost preferred filler is calcium carbonate having average particle sizeof 3-8 μm, preferably about 5 μm.

The resin system-catalyst component of the molding compound preferablyincludes any internal lubricant contemplated by one skilled in themolding compound art in an amount of from about 0.5 to about 2.3 weightpercent, based on the weight of the molding compound.

Cure inhibitors may be employed to retard the polymerization of theunsaturated polyester resin in the sheet molding compound. If cureinhibitors are employed in the resin system-catalyst component, themolding compound of the present invention preferably comprise no morethan about 0.3 weight percent of cure inhibitors in the resin-systemcatalyst component, based on the weight of the molding compound, andmore preferably, from about 0.01 to 0.2 weight percent. Suitable cureinhibitors include, but are not limited to,

-   -   substituted phenolic derivatives such as hydroquinone, quinone,        and para-benzoquinone; and    -   quaternary ammonium salts, especially of strong bases such as        trimethyl benzylammonium chloride or bromide.        In the present invention, the preferred cure inhibitor, when        used, is para-benzoquinone.

The additional monomer is separate from the co-curable monomer in theresin system, and, if used in the resin system-catalyst component, ispreferably present in an amount less than about 7.0 weight percent,based on the weight of the molding compound. Suitable monomers, include,but are not limited to, the monomers useable as the co-curableunsaturated monomer in the resin system.

Accelerators, may optionally be used to help reduce cure times.Accelerators, when used, act as additional classes of cure catalysts forthe unsaturated polyesters. Suitable compounds useable as acceleratorsinclude, but are not limited to, cobalt compounds such as cobaltnaphthenate and octanoate.

The thickener component of the molding compound preferably comprisesfrom about 0.2 to about 0.9 weight percent of a chemical thickener,based on the weight of the molding compound. Any suitable chemicalthickener contemplated by one skilled in the molding compound art may beused.

The thickener component of the molding compound may also contain otherknown molding compound additives including, but not limited to, pigment,monomer, cure inhibitor and internal lubricant.

The pigment may be any pigment contemplated by one skilled in themolding compound art. If pigment is used, it is preferred that thepigment be present in the molding compound in an amount of about 5weight percent or less, based on the weight of the molding compound.

The list of monomers useable in the thickener component includes, but isnot limited to, the monomers useable in the resin system component. Ifmonomer is used in the thickener component of the molding compound, itis preferred that the monomer in the thickener component be present inan amount of about 3 weight percent or less, based on the weight of themolding compound.

If an internal lubricant is used in the thickener component, theinternal lubricant may be any internal lubricant contemplated by oneskilled in the molding compound art, and is preferably present in thethickener component in an amount of about 1.3 weight percent or less,based on the weight of the molding compound.

If cure inhibitors are employed in the thickener component, the moldingcompound of the present invention preferably comprises no more thanabout 0.3 weight percent of cure inhibitors in the thickener component,based on the weight of the molding compound.

The molding compound of the present invention preferably comprises fromabout 15.0 to about 35.0 weight percent of fiber reinforcement, based onthe weight of the molding compound, and more preferably, from about 18.0to about 27.0 weight percent, and even more preferably, from about 19 toabout 22 weight percent.

The fiber reinforcement is approximately 2.5 cm long+/−1 cm. The longerlength of the fiber reinforcement differentiates sheet molding compoundfrom the bulk molding compounds and ZMC, and provides the strongermechanical properties relative to the comparable formulation of thesetwo other compounds. The fiber reinforcement is selected from a listincluding, but not limited to, fiberglass; carbon fiber; aramid fiber;lignocellulosic fibers; agricultural fibers; natural and synthetictextile fibers; olefinic fibers, including oriented olefinic fibers;mineral reinforcements with aspect ratios in excess of about 4; ormixtures of any or all of these reinforcements. Fiberglass is thepreferred fiber reinforcement, and is most preferable about 2.5 cm longchopped 23C fiberglass fiber such as is available from CertainTeed,Corp.

Having generally described the present invention, a furtherunderstanding can be obtained by reference to certain specific exampleswhich are provided herein for purposes of illustration only and are notintended to be limiting unless otherwise specified.

Example 1

A preferred molding compound of the present invention which is capableof producing door skins having thicknesses of between about 1.0 mm andabout 2.5 mm; widths of between about 0.75 m and about 1.07 m; andlengths of between about 1.95 m and about 2.45 m and having a shrinkageof between about −0.0003 to about +0.0015 comprises the following:

TABLE 1 WT % OF MOLDING ITEM COMPOUND Resin System-Catalyst ComponentResin system¹ 25.35 Mineral filler² 50.71 Cure catalyst³ 0.38 Cureinhibitor⁴ 0.05 Internal lubricant⁵ 1.18 Thickener component Thickener⁶0.38 Pigment⁷ 1.12 Monomer⁸ 0.28 Internal lubricant⁹ 0.54 CureInhibitor⁴ 0.01 Fiber reinforcement¹⁰ 20.0 ¹Alpha/Owens Corning E-4295(low profile resin system comprising a polyester resin, low profileadditives, and monomer) ²Huber ® W-4 from J. M. Huber Corporation,Engineered Materials Division, of Quincy, Illinois³t-Butylperoxybenzoate from Aztec Peroxides, Inc., of Elyria, Ohio⁴Ashland Mod-E (5% PBQ) from Ashland Chemical Co., Composite PolymersDivision, of Columbus, Ohio ⁵66 wt. % Norac Coad 10 calcium stearatefrom The Norac Co., Inc. of Azusa, California, and 34 wt. % zincstearate XM Powder HyDense ® of Mallinckrodt Speciality Chemicals Co.,of Chesterfield, Missouri ⁶PG-9033 from Plasticolors, Inc., of Astabula,Ohio ⁷CP-10028 from Alpha/Owens Corning of Guelph, Ontario, Canada⁸Vinyltoluene ⁹20 wt. % zinc stearate from the Synthetic Products, ofCleveland, Ohio, and 80 wt. % zinc stearate XM Powder HyDense ® ofMallinckrodt Speciality Chemicals Co., of Chesterfield, Missouri ¹⁰23Cfrom CertainTeed Corp., of Wichita Falls, Texas

The resin system is mixed, by techniques known in the art, with themineral filler, cure catalyst, internal lubricant and cure inhibitorbeing mixed in a low shear Ross mixer. Preferably, the resin system ismixed first with the cure catalyst, with the internal lubricant beingadded to the mixer next, followed by the mineral filler. The mixture istransferred to a high shear dynamic mixer, such as a Shar mixer or aFinn and Fram mixer. The thickener component is preferably prepared in aseparate mixer and is then transferred to the high shear dynamic mixerfor blending with the resin system-catalyst component.

A presently preferred embodiment employs a similar resin system and isprocessed similarly, except that during the molding process, vacuum isapplied while the resin is still flowable, to reduce blisters, and hencescrap. The resin system consists of 17.69 parts S 903-300, an inhibitedresin formulation containing a low profile additive, and containing thesame DCPD polyester base resin as E-4295, available from AOC, Guelph,Ontario; 7.02 parts T181 saturated polyester low profile additive; 0.37parts t-amylperoxybenzoate cure catalyst; 0.62 parts internal lubricant;and 49.41 parts mineral filler. The thickener component is the same asin Table 1, but used in an amount of 2.89 parts. This thickenercomponent is available from AOC as G 7304W. The glass fiberreinforcement is 22 parts PPG 5509 glass fiber available from PPG inShelby, N.C.

The preparation of sheets of sheet molding compound is known in the art.For example, Shannon and Denton describe a method of making moldingcompounds in U.S. Pat. No. 4,105,623, which is incorporated byreference. The mixture is removed from the high shear dynamic mixer andsupplied under pressure to a manifold that applies the paste to atraveling sheet of plastic transport film. Fiberglass roving is choppedto approximately 2.5 cm+/−1 cm lengths and sprinkled, in an essentiallyuniform manner, over the mixture as it continues to travel on theplastic transport film. A balancing layer of the mixture is applied froma second manifold in order to sandwich the chopped fiberglass layer. Thebalancing layer is covered by a plastic covering film forming a sheetmolding compound sheet. The entire sheet molding compound sheet iscompacted, thereby, enhancing the mixing of fiberglass and resin;allowed to maturate for about 2 days in special styrene transferresistant wrapping; and molded in a match compression mold atapproximately 148° C.-160° C. for about 70 seconds at approximately3.5-10.3 MPa of pressure to yield a door skin having a thickness ofbetween about 1.0 mm and about 2.5 mm; a width of between about 0.75 mand about 1.07 m; and a length of between about 1.95 m and about 2.45 m.

Assembly of door 10 of the present invention is completed by securing,in any suitable manner, and preferably with an adhesive, the first doorskin 24 to a first side of a frame 14 housing a core 12, and the secondskin 26 to a second side of the frame. The combined thickness of thedoor skins 24 and 26, core 12 and frame 14 ranges is preferably fromabout 1.375-2.5 inches.

Example 2 and Comparative Examples A and B

Example 2 is a mixture prepared according to the sheet molding compoundin Example 1. Comparative Example A is prepared from a sheet moldingcompound comprising a resin system having a polyester resin, two lowshrinkage additives and no low profile additives. Comparative Example Bis prepared for a sheet molding compound having a polyester resin, onelow shrinkage additive, and only one low profile additive. The polyesterresin in Example 1 is different from the polyester resin in ComparativeExample A, but is the same as the polyester resin in Comparative ExampleB. The low profile additive in Comparative Example B is the same as alow profile additive in Example 1.

The shrinkage of cured plaques of the sheet molding compounds of Example2 and Comparative Examples A and B, as compared to the mold they weremolded in, was measured at room temperature. The plaques were molded tobe planar and have an average thickness of about 3.2 mm and dimensionsof about 304.8 mm×304.8 mm. A check fixture with dial indicators wasmade to check the plaques. A calibration gauge was used to zero thefixture to the size of the mold. The molded plaques were allowed to setat least one day before being measured. Each plaque was measured in fourlocations, two in the transverse and two in the longitudinal direction.Each dial reading was divided by the length of the plaque to get theshrinkage value. Table 2 displays the shrinkage for each of the plaques.

TABLE 2 Cured Sheet Molding Compound Plaque Shrinkage Example 2 −0.0002Comparative Example A −0.0007 Comparative Example B −0.0004

The surfaces of the plaques were analyzed by a Loria® surface analyzer.The plaques were molded in a flat mold in which the show surface hadbeen highly polished to a mirror finish. The Loria® surface analyzerreflected a laser beam off the surface of the object. The laser beam wasmoved across the surface of the plaques in a series of parallel linesover an area of about 279.4 mm×279.4 mm. The reflected beam is projectedunto a reflective screen. The image is then picked up off the screen bya high-resolution video camera. The images of these lines were thenanalyzed for smoothness. From this analysis, the long term Loria® numberand the orange peel Loria® number were obtained. With long term Loria®number, the smaller the number, the smoother the surface. With orangepeel Loria® number, the scale is 0-10, with 10 being the smoothestsurface. Table 3 displays the long term and orange peel Loria® numberfor each of the plaques.

TABLE 3 Comparative Comparative Property Example 2 Example A Example BLong Term Loria ® 119 I.A. I.A. Number Orange Peel Loria ® 8.2 7.5 6.3Number I.A. indicates that an accurate reading could not be attained.

The long term Loria® number for Comparative Examples A and B could notbe accurately obtained. This indicates that the sheet molding compoundsused to make the plaques of Comparative Examples A and B producedsurfaces which were too dull to enable the Loria® surface analyzer torecord accurate reading. The Loria® surface analyzer can only attain anaccurate long term Loria® number readings for samples having a long termLoria® numbers below about 250. Thus, it can be concluded that the longterm Loria® number of the plaques of Comparative Examples A and B areabove about 250.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which the invention relateswill appreciate other ways of carrying out the invention defined by thefollowing claims.

1-4. (canceled)
 5. A molding compound for preparing a door skincomprising: a) a resin system present in an amount from about 16 toabout 33.5 weight percent, including: i) a curable resin; ii) aco-curable unsaturated monomer; and iii) at least one low profileadditive; b) filler material present in an amount from about 30 to about70 weight percent; and c) fiber reinforcement material present in anamount from about 15 to about 35 weight percent.
 6. The molding compoundof claim 5, wherein the resin system is present in an amount from about21 to about 29 weight percent.
 7. The molding compound of claim 5,wherein the filler material is present in an amount from about 48 toabout 65 weight percent.
 8. The molding compound of claim 5, wherein thefiber reinforcement is present in an amount from about 18 to about 27weight percent.
 9. The molding compound of claim 5, wherein the curableresin is a polyester resin.
 10. The molding compound of claim 9, whereinthe curable polyester resin comprises a highly reactive unsaturatedpolyester resin.
 11. The molding compound of claim 9, wherein thecurable polyester resin is selected from the group consisting of highreactivity orthophthalic polyester resins, high reactivity isophthalicpolyester resins, and high reactivity dicyclopentadiene-modifiedpolyester resins.
 12. The molding compound of claim 5, wherein theco-curable unsaturated monomer is selected from the group consisting ofalkylacrylates, alkylmethacrylates, vinyltoluene, α-methylstyrene,p-methylstyrene, and styrene.
 13. The molding compound of claim 5,wherein the low profile additive is selected from the group consistingof polyvinyl acetate, modified polyvinyl acetate, saturated polyester,modified saturated polyester, polymethyl methacrylate, polyurethanes,styrenic block copolymer-modified rubber, and saturated glycol-C₂ to C₆dicarboxylic acid polyesters.
 14. The molding compound of claim 5,wherein the resin system comprises at least two low profile additives.15. The molding compound of claim 5, wherein the filler materialcomprises calcium carbonate.
 16. The molding compound of claim 5,wherein the fiber reinforcement material comprises fiberglass.
 17. Themolding compound of claim 14, wherein the curable resin comprises a highreactivity dicyclopentadiene-modified polyester, the co-curableunsaturated monomer comprises styrene, and the low profile additivescomprise a saturated glycol-C₂ to C₆ dicarboxylic acid polyester and amodified polyvinyl acetate.
 18. A molding compound capable of producinga door skin prepared by a process comprising the steps of: a) preparinga resin system-catalyst component by mixing: i) a resin system presentin an amount from about 16 to about 33.5 weight percent, based on theweight of the molding compound, including a curable resin; a co-curableunsaturated monomer; and at least one low profile additive; ii) a fillermaterial present in an amount from about 30 to about 70 weight percent,based on the weight of the molding compound; b) preparing a thickenercomponent comprising chemical thickener present in an amount from about0.2 to about 0.9 weight percent, based on the weight of the moldingcompound; c) combining the resin system-catalyst component and thethickener component; and d) adding a fiber reinforcement componentpresent in an amount from about 15 to about 35 weight percent, based onthe weight of the molding compound, to the combined resin-catalystcomponent and the thickener component to form the molding compound. 19.The molding compound of claim 18, wherein the resin system is present inan amount from about 21 to about 29 weight percent, based on the weightof the molding compound.
 20. The molding compound of claim 18, whereinthe filler material is present in an amount from about 48 to about 65weight percent, based on the weight of the molding compound.
 21. Themolding compound of claim 18, wherein the fiber reinforcement componentis present in an amount from about 18 to about 27 weight percent, basedon the weight of the molding compound.
 22. The molding compound of claim18, wherein the curable resin comprises a curable polyester resin. 23.The molding compound of claim 22, wherein the curable polyester resin isselected from the group consisting of high reactivity orthophthalicpolyester resins, high reactivity isophthalic polyester resins, and highreactivity dicyclopentadiene-modified polyester resins.
 24. The moldingcompound of claim 18, wherein the co-curable unsaturated monomer isselected from the group consisting of allylacrylates,alkylmethacrylates, vinyltoluene, α-methylstyrene, p-methylstyrene, andstyrene.
 25. The molding compound of claim 18, wherein the low profileadditive is selected from the group consisting of polyvinyl acetate,modified polyvinyl acetate, saturated polyester, modified saturatedpolyester, polymethyl methacrylate, polyurethanes, styrenic blockcopolymer-modified rubber, and saturated glycol-C₂ to C₆ dicarboxylicacid polyesters.
 26. The molding compound of claim 18, wherein the resinsystem-catalyst component further comprises one or more of a curecatalyst, a cure inhibitor, and an internal lubricant.
 27. The moldingcompound of claim 18, wherein the thickener component further comprisesone or more of a monomer, a cure inhibitor, a pigment, and an internallubricant.
 28. The molding compound of claim 18, wherein: the resinsystem is present in an amount from about 21 to about 29 weight percent,based on the weight of the molding compound; the curable resin comprisesa high reactivity dicyclopentadiene-modified polyester; the co-curableunsaturated monomer comprises styrene; the at least one low profileadditive comprise a saturated glycol-C₂ to C₆ dicarboxylic acidpolyester and a modified polyvinyl acetate; the resin system-catalystcomponent further comprises a cure catalyst, a cure inhibitor, and aninternal lubricant; the filler material comprises calcium carbonate andis present in an amount from about 48 to about 65 weight percent, basedon the weight of the molding compound; the thickener component furthercomprises a monomer, a cure inhibitor, a pigment, and an internallubricant; and the fiber reinforcement component comprises fiberglassand is present in an amount from about 19 to about 22 percent.